Posterior atrophic jaws rehabilitated with prostheses supported by 5 × 5 mm implants with a nanostructured calcium-incorporated titanium surface or by longer implants in augmented bone. 3-year results from a randomised controlled trial.

Purpose: To evaluate whether 5.0 × 5.0 mm dental implants with a novel nanostructured calcium-incorporated titanium surface could be an alternative to implants of at least 10.0 mm long placed in bone augmented with bone substitutes in posterior atrophic jaws.

Materials and methods: Forty patients with atrophic posterior (premolar and molar areas) mandibles with 5.0 mm to 7.0 mm bone height above the mandibular canal, and 40 patients with atrophic maxillas with 4.0 mm to 6.0 mm below the maxillary sinus, were randomised according to a parallel group design to receive between one and three 5.0 mm implants or one to three at least 10.0 mm-long implants in augmented bone at two centres. All implants had a diameter of 5.0 mm. Mandibles were vertically augmented with interpositional bovine bone blocks covered with resorbable barriers. Implants were placed after 4 months. Maxillary sinuses were augmented with particulated porcine bone via a lateral window covered with resorbable barriers, and implants were placed simultaneously. All implants were submerged and loaded after 4 months with provisional prostheses. Four months later, definitive screw-retained or provisionally cement metal-ceramic or zirconia prostheses were delivered. Patients were followed to 3 years post-loading and the outcome measures were: prosthesis and implant failures, any complication, and peri-implant marginal bone level changes.

Results: Seven patients dropped out before the 3-year evaluation (two short mandibles, one short maxilla, two augmented mandibles and two augmented maxillae). In mandibles, two grafted patients were not prosthetically rehabilitated because of multiple complications and two implants failed in the same patient (the second was a replacement implant) vs one patient who lost a short implant and crown 2 years after loading. In maxillas one short implant failed with its provisional crown 3 months post-loading. There were no statistically significant differences in prostheses (difference in proportion = 0.001; 95% CI: -0.12 to 0.13; P = 1.000) and implant failures (difference in proportion = 0.00; 95% CI: -0.13 to 0.13; P = 1.000) up to 3 years after loading. Significantly, more complications occurred at mandibular grafted sites: 17 augmented patients were affected by complications vs eight patients treated with short implants in mandibles (difference in proportion = 0.43; 95% CI: 0.13 to 0.64; P = 0.008). In the maxilla, six sinus-lifted patients vs two patients treated with short implants were affected by complications; the difference not being statistically significant (difference in proportion = 0.21; 95% CI: -0.05 to 0.45; P = 0.232). Patients with mandibular short implants lost on average 1.10 mm of peri-implant bone at 3 years and patients with 10.0 mm or longer mandibular implants lost 1.39 mm. Patients with maxillary short implants lost on average 1.04 mm of peri-implant bone at 3 years and patients with 10 mm or longer maxillary implants lost 1.43 mm. Longer implants showed a greater bone loss up to 3 years after loading than short implants both in maxillae (mean difference: -0.39 mm; 95% CI: -0.70 to -0.07 mm; P = 0.017) and in mandibles (mean difference: -0.29 mm; 95% CI: -0.53 to -0.05 mm; P = 0.020).

Conclusions: Three years after loading, 5.0 mm × 5.0 mm implants achieved similar results than longer implants placed in augmented bone. Short implants might be a preferable choice to bone augmentation especially in posterior mandibles since the treatment is faster, cheaper and associated with less morbidity. However, 5- to 10-year post-loading data are necessary before making reliable recommendations.